Products intended for this particular field of activity have to satisfy very stringent requirements.
First of all, they have to show satisfactory storage properties and, in particular, should be largely unaffected by moisture. Accordingly, they should be substantially non-hygroscopic. In addition, since these products consist of a mixture of sugar and cocoa, which are two elements of different density, they should show no signs of separation as a function of time through differential sedimentation of the sugar and cocoa which would take the densest products to the bottom of the storage tank.
Secondly, since these products are intended for use in existing machines, they have to show predetermined and reproducible flow characteristics to ensure that a constant and predetermined dose of the products is always dispensed without any need to modify the setting of the dosing units. The dosing units typically used are, for example, of the Spengler or Wittenborg type which are set up to deliver reproducible doses, for example of 25 g, from the products normally sold in these machines.
Thirdly, the products have to dissolve instantly in hot water without the beverage having to be stirred, for example with a spoon.
Finally, all these characteristics have to be obtained using predetermined compositions.
The products typically used consist of a dry mixture of crystallized sugar and cocoa powder with, optionally, milk powder and such additives as salt or vanilla extract.
Accordingly, these products inevitably have a pronounced tendency towards differential sedimentation. In addition, the free sugar is extremely sensitive to moisture which presents storage problems.
Canadian Pat. No. 1,073,732 describes a process in which a very fine sugar having a particle size below 250 m is moistened with 3% water, a mixture of cocoa and additives is separately prepared, after which the sugar and the mixture are introduced into a mixer heated to a temperature of 50.degree. C. to 90.degree. C. at a heating rate of 1.5.degree. C. to 13.degree. C. per minute. The product is then rapidly cooled and reduced to powder with a final density of 500 to 600 g per litre and a particle size distribution in which 100% of the product is smaller than 840 .mu.m in size and 60% is larger than 250 .mu.m in size.
In the cited document, the density mentioned corresponds to what is conventionally called the poured apparent voluminal mass. This is because it is standard practice to distinguish between the poured apparent voluminal mass calculated with a powder which has just been poured into a graduated container and the free apparent voluminal mass calculated with a powder compacted after tapping 100 times. Futher particulars of the poured and free apparent voluminal masses can be found in FIL (Federation Internationale de Laiterie) Standard No. 134:1986 which explains the exact methods. In the following description, the poured and free apparent voluminal masses were measured by the method specified in that Standard.
The product obtained by the method described in Canacian Patent No. 1,073,732 has a major problem. This is because it is not possible to obtain any reproducibility in the flow of this product, the conditions governing its flow definitely not being controlled, even remotely, in this document. This is, after all, normal because the product in question is not inended for use in an automatic dispenser, as reflected in the use of a spoon for dosing and in the use of hot milk, which are two methods which simply could not be considered in the context of an automatic dispenser.